Particle accelerator



Sept. 20, 1966 J. PINEL ETAL 3,274,502

PARTIGLE ACCELERATOR Filed Dec. 21, 1962 2 Sheets-Sheet 1 C I a w.

, FIGZ I NV ENTORS G-MDUR/ER 21 J PINEL ATTORNEY Sept. 20, 1966 J. PINELETAL 3,274,502

PARTICLE ACCELERATOR Filed Dec. 21, 1962 2 Sheets-Sheet 2 1O FIG.4 9 6INVENTORS G-HOl/RIER d J- PINEL ATTORNEY United States Patent 3,274,502PARTICLE ACCELERATOR Jacques Pinel and Georges Mourier, Paris, France,as-

signors to CSF Compagnie Generale de Telegraphic Sans Fil, Paris, FranceFiled Dec. 21, 1962, Ser. No. 246,449 Claims priority, applicationFrance, Jan. 10, 1962, 884,375, Patent 1,318,737; May 3, 1962, 896,281 8Claims. (Cl. 328234) The present invention relates to acceleratordevices for charged particles, such as protons, etc., and moreparticularly relates to accelerators of the cyclotron type.

In the cyclotrons, the particles describe spirally-shaped paths ortrajectories on the inside of an accelerating chamber composed of twosemicylindrical throughs usually called Ds or Dees, separated by aslight interval, the form of the trajectories as paths being due to theaction (1) of a direct-current or constant magnetic field which impartsto the particles a circular movement with a radius proportional to thespeed thereof, and (2) of a high-frequency electric field, establishedbetween the'two Us in such a manner as to accelerate the particles whilethey pass from one D to the other.

With such classical arrangement, the accelerating action of the highfrequency extends therefore only over a minute portion of an entirecycle of the trajectory, that is of the period during which a particledescribes 'a complete angle of 21r.

The present invention has for its object an improved cyclotron,characterized by a new arrangement in which the charged particles aresubjected to the action of a highfrequency electric field during theentire duration of the trajectories or paths thereof, or at least duringthe major portion of these trajectories.

Consequently, a cyclotron according to the present invention, whichcomprises an accelerating chamber placed within the air gap of anelectromagnet, a source of charged particles on the inside of theaccelerating chamber, and means for accelerating the particles with theaid of a high-frequency electric field perpendicular to the magneticfield produced by the electromagnet, is characterized by an arrangementenabling the said electric field to exert its effect throughout theentire space comprising the trajectories of the particles or at leastwithin the major portion of this space.

In the novel arrangement according to the present invention theaccelerating chamber is no longer divided into separate Us or Dees.

According to a preferred mode of construction of the present invention,the high-frequency electric field is produced on the inside of theaccelerating chamber with the aid of a delay structure coupled in anysuitable manner to a high-frequency generator.

A cyclotron thus modified in accordance with the teachings of thepresent invention presents a certain number of advantages andparticularly an improved output and a current of utilizable particles ofincreased density due to the fact, in contrast to the classicalconstructions of cyclotrons, that the novel arrangement according to thepresent invention assures to the flux or flow of particles an importantand significant phase focusing action.

Accordingly, it is an object of the present invention to provide aparticle accelerator, particularly of the cyclo tron type, which assuresan improved output as compared to that realizable with the known priorart constructions.

It is another object of the present invention to provide a cyclotron.particle accelerator in which the particles are subjected along most ifnot all the trajectories or paths thereof to a high-frequency electricfield thereby improving the performance of the device.

Still another object of the present invention resides in the provisionof a cyclotron-type particle accelerator which is simple inconstruction, obviates the need for separated Dees and permits asignificant phase focusing within the particle flux.

These and other objects, features and advantages of the presentinvention will become more obvious from the following description whentaken in connection with the accompanying drawing which shows, forpurposes of illus tration only, several embodiments in accordance withthe present invention, and wherein FIGURE 1 is a schematic crosssectional view through a cyclotron according to the present invention,taken along line II of FIGURE 2;

FIGURE 2 is a schematic cross sectional view through the cyclotronillustrated in FIGURE 1, taken along line IIII of FIGURE 1;

FIGURE 3 is a perspective view illustrative of the known prior artsector focusing systems in relativistic cyclotrons;

FIGURE 4 is a schematic cross sectional view through a relativisticcyclotron according to the present invention,

taken along line IVIV of FIGURE 5;

FIGURE 5 is a schematic cross sectional view of the relativisticcyclotron illustrated in FIGURE 4, and taken along line VV of FIGURE 4,and

FIGURE 6 is a cross sectional view of a modified embodiment of arelativistic cyclotron according to the present invention.

Referring now to the drawing wherein like reference numerals are usedthroughout the various views to designate like par-ts, and moreparticularly to FIGURE 1 and 2, there is illustrated in these twofigures an accelerating chamber 1 of parallellepipedic form, evacuatedand placed within the air gap of an electromagnet 2 having pole pieces 3and 4 of circular cross section.

To the inside of the accelerating chamber 1 are secured two series ofarrays 5 and 6 of straight, parallel, metallic bars forming a waveguiding or wave delaying structure.

A source of charged particles, for example, protons,

schematically illustrated in the drawing and designated therein byreference numeral 7, is disposed between these two arrays 5 and 6 withinthe central region of the chamber 1.

The delay structure which is composed of the two arrays 5 and 6, iscoupled to a conventional high frequency generator (not illustrated)which produces a signal having a wavelength x.

The electromagnet 2 is realized, as in the conventional cyclotrons, insuch a manner, as to supply a magnetic field H satisfying the relationw: (e/m)H, which e and m are, respectively, the charge and the mass ofthe particles, and w=21rF, F being the frequency corresponding to theutilized wavelength )t.

By having recourse to a wellknown technique, the two arrays 5 and 6 areexcited in the fundamental mode, that is the O-mode, and the necessarysteps are taken to obtain between the points A and B a stationary wave,preferably with a node at the center and antinodes of voltage at the twoextremities.

One realizes thus within the space comprised between the two series ofbars 5 and 6 a high frequency electric field, directed alternately fromA toward B and from B toward A of which the intensity varies at thefrequency F.

The charged particles, designated in the drawing by reference numeral 8,are therefore subjected, on the one hand, to the action of the magneticfield of the electromagnet 2, exactly as in conventional classiccyclotrons, and, on the other, according to the present invention, tothe permanent action of a high frequency field of which the lines offorce are perpendicular to the magnetic field, the action of the highfrequency field being effective throughout the entire space covered bythe particles, or at least within the major portion of the space.

Under these conditions, the paths or trajectories of the particleswithin the accelerating chamber deviate within a certain measure fromthe regular spiral form of the classic cyclotrons but, in return, bothcalculations and tests show that there is produced instead a veryimportant phase focusing effect.

It is necessary in that connection to recall that in the classiccyclotrons the particles present within the accelerating chamber do notall have an identical fate. Those among the particles which traverse theinterval separating the Dees exactly at the moment at which thehigh-frequency field manifests itself therein with the maximum intensityand in the proper direction, that is in the same direction as themovement of the particles, are accelerated under the best conditions. Onthe other hand, those of the particles which arrive slightly ahead orslightly after this optimum moment are accelerated to a lesser degree.The particles which arrive thereat when the high frequency field becomeszero prior to the reversal of its direction do not undergo of course anymodifications in speed, and finally those which arrive later in time andencounter a field of direction opposed to the movement thereof areobviously decelerated. It follows from these phase differences of thevarious particles that only a portion among them normally finds itselfregularly accelerated and are able to reach the output of the cyclotron.Hence, one normally obtains an output from the overall installation ofthe prior art system that is relatively little satisfactory.

In the improved cyclotron according to the present invention, theelectric field is present all along the trajectories of the chargedparticles on their movement in the acceleration chamber. At each pointof the trajectory the electric field may be considered as thegeometrical sum of a tangential component, which is tangent to thetrajectory, and a centrifugal or radial component which is perpendicularto the tangential component. This radial component of the high frequencyelectric field increases the tangential speed of the particles delayedwith respect to those of optimum phase and diminishes those particleswhich are ahead. The particles thereby group themselves into chapeletsabout those among them which have the best phase, and the ratio of thenumbers of particles used to nonused particles is considerably increasedin comparison with what has been noted in cyclotrons known heretofore.

The described arrangement according to the present invention thereforeprovides an improved output and permits the realization of particlecurrents with an increased intensity.

The present invention is applicable to cyclotrons of all energies.Nevertheless, the present invention presents a particular interest inthe case of so-called relativistic cyclotrons in which the particlesacquire very high energies rendering the relativistic variation of themass thereof non-negligible.

It is known that in the relativistic cyclotrons the dual difiiculty offocusing the accelerated particles and to maintain the movement thereofin phase With the high frequency accelerating field has been resolved ina satis factory manner by the use of a magnetic field having alternategradients. A well-known realization of this principle is the so-calledsector focusing system which consists of adding to the pole pieces ofthe magnet or of the electromagnet ferromagnetic sectors, generallycurved in spiral shape and separated by intervals of the same shape,whereby the common apex of all the sectors is located at the center ofthe pole pieces. There are thus produced between the pole pieces, zoneswith a strong field, so-called hills or crests alternating with zoneswith a weak field, so-called valleys whereby the air gap is shorter inthe former than in the latter.

The focusing is therefore realized in prior art relativistic cyclotronsby a modification of the structure of the pole pieces of the magnet orof the electromagnet of the primitive cyclotron, that is, of thenonrelativistic cyclotron.

Within a cyclotron according to the present invention, it is possible toproduce a magnetic field with alternating gradients or zones Withoutmodifying the pole pieces but by arranging the accelerating chamber, andmore particularly the delay structure disposed within this chamber in anappropriate manner.

Since the delay structure is composed of bars made of non-ferrous metal,which is a good conductor of electricity, the improvement according tothe present invention consists in utilizing hollow bars containing onthe inside thereof pieces of ferromagnetic metal in such a manner as tocreate within the accelerating chamber zones with iron to obtain arelatively strong magnetic field alternating With zones Without iron toobtain a relatively Weak magnetic field.

FIGURE 3 illustrates the known principle of sector focusing by showingin perspective view a .pole piece 11 on which are fixed sectors offerromagnetic metal 12, separated by intervals 13. Facing the sectors 12are obtained zones having relatively strong field or hills, and facingthe intervals 13 are obtained zones with a relatively weak field orso-called valleys.

FIGURE 4 which is a cross sectional view taken along line IV-IV ofFIGURE 5, and FIGURE 5 which is a. cross sectional view along line V--Vof FIGURE 4 illustrate in what manner a substantially sector focusing isrealized in a cyclotron according to the present invention. In this typeof cyclotron, the accelerating chamber 1 encloses a delay structurecomposed of two superposed arrays of bars 5 and 6, made of non-ferrousmetal, that is a good electrical conductor, such as, for example, cop-The bars 5 and 6 are hollow, and on the inside thereof are disposedferromagnetic pieces 9, the length of the various pieces and theposition thereof being chosen in such a manner as to fill zones definedby spirally-curved sectors. The common apex or point of intersection ofthe sectors is located within the axis of the accelerating chamber 1which is also the axis of the pole pieces of which the surface isindicated by the circle 10 in dash lines.

With such an arrangement, the lines of force of the magnetic field,produced by the pole pieces of the magnet encounter within theaccelerating chamber zones alternately with and without iron, which inturn, causes the intensity of the magnetic fiux to have alternately verystrong and very weak values that is hills or crests for those spaceswith iron and valleys for those without iron. One obtains thus afocusing that is substantially equivalent to that supplied by the knownsystem illustrated in FIG- URE 3.

In the modified embodiment illustrated in FIGURE 6, the hollow tubes 5and 6 are filled with ferromagnetic cores along the entire lengththereof except within the central zone of the accelerating chamber,indicated by the circle shown in dash lines in the drawing.

This embodiment does not show a sector focusing such as FIGURES 4 and 5but the arrangement of FIGURE 6 is of great simplicity and permitsproduction of a magnetic field with alternating gradients or zonesfurnishing a very satisfactory focusing action in relativisticcyclotrons.

It should also be noted that there also exists an interest with theembodiment of FIGURE 6 to diminish progressively the transverse crosssection of the ferromagnetic cores at the end or extremities adjacentthe central zone of the chamber in order to render progressive thevariation of the field between the zone with iron and the zone withoutiron.

Irrespective of the particular construction, it may be readily seen thatthe present invention permits utilization of shorter air gaps than thoseconstituted by the pole pieces according to FIGURE 3. However, it isknown that the reduction of the air gap permits a reduction also of thegeneral dimensions of the magnet and further leads to an appreciableeconomy in the cost of production and ovenall dimensions of theinstallation.

While We have shown and described several embodiments in accordance withthe present invention, it is understood that the same is not limitedthereto but is susceptible of numerous modifications and changes asknown to a person skilled in the art, and we therefore do not wish .tobe limited to the detail shown and described herein but intend to coverall such changes and modifications as are encompassed by the scope ofthe appended claims.

We claim:

1. A cyclotron comprising: an acceleration chamber,

a source of charged particles located substantially within the center ofsaid chamber, first means for establishing within said chamber aconstant unidirectional magnetic field, and second means forestablishing a high frequency electric field substantiallyperpendicularly to said magnetic field substantially within the entireinteror space of said chamber including a wave delaying structuredisposed within said chamber, and a source of high frequency coupled tosaid delay structure, said delay structure including two series ofsubstantially parallel bars disposed adjacent to substantially theentire path of said charged particles in planes on either sides thereofsubstantially perpendicular to said magnetic field.

2. A cyclotron comprising: an acceleration chamber, a source of chargedparticles located substantially Within the center of said chamber, firstmeans for establishing within said chamber a constant magnetic field,and second means for establishing a high frequency electric fieldsubstantially perpendicularly to said magnetic field substantiallywithin the entire interior space of said chamber including a wavedelaying structure disposed within said chamber, and a source of highfrequency energy coupled tosaid delay structure, said delay structureincluding two series of substantially parallel bars made of a nonferronsmetal and disposed in two planes substantially perpendicular to saidmagnetic field, said bars being hollow, and predetermined portionsthereof being filled with ferromagnetic cores to form within theacceleration chamber zones with iron alternating with zones without ironwhereby the magnetic field configuration has alternate zones ofrelatively high and low intensities, respectively.

3. A cyclotron comprising: an acceleration chamber, a source of chargedparticles located substantially Within the center of said chamber, firstmeans for establishing within said chamber a constant magnetic field,and second means for establishing a high frequency electric fieldsubstantially perpendicularly to said magnetic field substantiallywithin the entire interior space of said chamber including a wavedelaying structure disposed within said chamber, and a source of highfrequency energy coupled to said delay structure, said delay structureincluding two series of substantially parallel bars made of a nonferronsmetal and disposed in two planes substantially perpendicular to saidmagnetic field, said bars being hollow, and predetermined portionsthereof being filled with ferromagnetic cores to form within theacceleration chamber zones with iron alternating with zones without ironwhereby the magnetic field configuration has alternate zones ofrelatively high and low intensities, respectively, and said zones beingsubstantially sector-shaped. so as to provide a sector-type focusingsuitable for use in relativistic cyclotrons.

4. A cyclotron comprising an acceleration chamber, a source of chargedparticles located substantially within the center of said chamber, firstmeans for establishing within said chamber a constant magnetic field,and second means for establishing .a high frequency electric fieldsubstantially perpendicularly to said magnetic field substantiallyWithin the entire interior space of said chamber including a wavedelaying structure disposed within said chamber, and a source of highfrequency energy coupled to said delay structure, said delay structureincluding two series of substantially parallel bars made of a nonferronsmetal and disposed in two planes perpendicular to said magnetic field,said bars being hollow, and predetermined portions thereof disposedoutside of the central area of said chamber being filled withferromagnetic cores to form within the acceleration chamber zones withiron and at least one zone without iron whereby the magnetic fieldconfiguration has zones of relatively high and low intensities,respectively.

5. A cyclotron comprising: an acceleration chamber, means providing asource of charged particles within said chamber, and means foraccelerating the particles within said chamber while simultaneouslytherewith producing a phase focusing action including first means forestablishing within said chamber a magnetic field and second meanshaving a wave guiding structure for establishing a high frequencyelectric field substantially perpendicularly to said magnetic field withsaid electric field prevailing at least throughout the major portion ofthe interior space of said chamber through which move said particles,and means including said wave guiding structure for produc ing strongand weak Zones in said magnetic field.

6. A cyclotron comprising: an acceleration chamber, means effectivelyproviding a source of charged particles approximately within the centerof said chamber, first means for establishing within said chamber -amagnetic field, and second means for establishing a high frequencyelectric field substantially perpendicularly to said magnetic fieldthroughout at least a major portion of the interior space of saidchamber including a wave guiding structure made of a material that issubstantially non-magnetic and good electrical conductor, and meansassociated with said wave guiding structure for effectively providingwithin the acceleration chamber zones of relatively high and lowmagnetic field intensities.

7. A cyclotron comprising: an acceleration chamber, mean-s providing asource of charged particles within said chamber, and means foraccelerating the particles within said chamber while simultaneouslytherewith producing a phase focusing action including first means forestablishing within said chamber a magnetic field and second meanshaving a wave guiding structure for establishing a high frequencyelectric field substantially perependicularly to said magnetic fieldwith said electric field prevailing at least throughout the majorportion of the interior space of said chamber through which move saidparticles, and means including said wave guiding structure for producingstrong and weak zones in said magnetic field with substantially uniformair gaps.

8. A cyclotron comprising: an acceleration chamber, means forestablishing within said chamber a constant unidirectional magneticfield, a wave guiding structure composed of two arrays of straight,substantially parallel, metallic bars disposed within said chamber intwo planes substantially perependicular to said magnetic field, a sourceof charged particles located substantially within the center of saidchamber between said two planes, and a source of high-frequency energycoupled to said wave guiding structure for establishing between the barsof each array a highfrequency electric field perpendicular to the barsand substantially perependicular to said magnetic field.

References Cited by the Examiner UNITED STATES PATENTS 2,229,572 1/1941Jonas 313-62 X 2,579,315 12/1951 Gurewitsch 3 l362 X 2,881,348 4/1959Palluel 3153.6 2,926,279 2/1960 Gallop 31539.3 X 2,933,639 4/1960 Lally315-3.6 3,129,356 4/1964 Phillips 315--3.5 X

JAMES W. LAWRENCE, Primary Examiner.

DAVID J. GALVIN, GEORGE N. WESTBY, Examiners.

R. DZIURGOT, R. JUDD, Assistant Examiners.

1. A CYCLOTRON COMPRISING: AN ECCELERATION CHAMBER, A SOURCE OF CHANGEDPARTICLES LOCATED SUBSTANTIALLY WITHIN THE CENTER OF SAID CHAMBER, FIRSTMEANS FOR ESTABLISHING WITHIN SAID CHAMBER A CONTANT UNDIRECTIONALMAGNETIC FIELD, AND SECOND MEANS FOR ESTABLISHING A HIGH FREQUENCYELECTRIC FIELD SUBSTANTIALLY PERPENDICULARLY TO SAID MAGNETIC FIELDSUBSTANTIALLY WITHIN THE ENTIRE INTERIOR SPACE OF SAID CHAMBER INCLUDINGA WAVE DELAYIUNG STRUCTURE DISPOSED WITHIN SAID CHAMBER, AND A SOURCE OFHIGH FREQUENCY COUPLED TO SAID DELAY STRUCTURE, SAID DELAY STRUCTUREINCLUDING TWO SERIES OF SUBSTANTIALLY PARALLEL BARS DISPOSED ADJACENT TOSUBSTANTIALLY THE ENTIRE PATH OF SAID CHARGED PARTICLES IN PLANES ONEITHER SIDES THEREOF SUBSTANTIALLY PERPENDICULAR TO SAID MAGNETIC FIELD.